The invention relates to a can lid and to a method for sealing a can with a lid.
Can lids having a lid ring and a lid membrane are known from the prior art, for example, from the German Laid-Open Specification 196 20 448 A1. Can lids of this type consist of a lid ring that is made by deep-drawing and punching from a coated sheet-metal blank, e.g. from tin plate, chromium-plated sheet metal or aluminum. An outer flange is provided on the outer edge of the lid ring for the later formation of a double fold and the inner edge of the lid ring has an annular flange which surrounds a lid opening. The annular flange can, for example, be formed by a flattened roll of the inner edge of the lid ring.
To seal a can with a lid of this type, the peripheral area of a lid membrane is fastened so as to be flat, for example, by heat-sealing or gluing, to the upper side of the annular flange pointing away from the inside of the can. The lid membrane thus seals the lid opening which extends over the entire area surrounded by the narrow lid ring. To open the can lid, a pull-open tab is attached to the upper side of the lid membrane. By pulling this tab, the fastening of the lid membrane on the annular flange can be released and the lid membrane pulled off from the lid ring in this way.
To prevent corrosion, the sheet-metal blank from which the lid ring and the lid membrane are made is coated on both sides. In the event that the lid membrane is fastened to the annular flange of the lid ring by means of heat-sealing, the sheet-metal blank is coated with a heat-sealable coating on the one side and provided with an anticorrosive coating on the other side. According to the manufacturing process known from DE 196 20 448, the lid membrane and the lid ring are formed from this sheet-metal blank which is coated on both sides by punching and shaping from the sheet-metal blank. During the punching process, cuts result at the ends on the outer periphery of the lid membrane and on the inner periphery and outer periphery of the lid ring. These cuts are not provided with a coating, so that they are exposed to corrosion.
For these reasons, the can lids made according to the known method tend to corrode at the end faces of the lid ring and the lid membrane, in particular during long storage.
Furthermore, the end face of the lid membrane has sharp edges which could result in injuries when pulling the lid membrane off from the lid ring.
Furthermore, it was also shown in the known can lids that the pull-open tab for removing the lid membrane from the lid ring is not fastened firmly to the lid membrane. Conventionally, the pull-open tab is fastened to the upper side of the lid membrane by heat-sealing or gluing. To ensure sufficient adherence to prevent the pull-open tab from coming undone during the removal process, it is necessary to connect the pull-open tab as extensively as possible with the lid membrane. However, an extensive connection results in a reduction in leverage when the lid membrane is pulled off from the lid ring, so that increased pull-off forces are required.
Thus, the object of the present invention is to provide an improved can lid of the aforementioned type.
Advantageously, such a can lid can result in reduced risk of injury during normal handling and is resistant to corrosion.
Therefore, in one aspect, the invention provides a can lid comprising a lid ring, for surrounding a lid opening, having on its inner periphery an annular flange configured as a flattened roll. The annular flange terminates at an end face. The annular flange end face is directed radially outward with respect to the lid opening. The can lid further comprises a lid membrane having a peripheral area terminating in an end face, which peripheral area is folded under toward the annular flange. The lid membrane is positioned on the lid ring for sealing the lid opening so as to be flat and so that the end face of the annular flange and the end face of the lid membrane abut one another.
Advantageously, the lid ring and the lid membrane are formed by punching and shaping from a sheet-metal blank coated on both sides.
In one aspect, the sheet-metal blank has a heat-sealable coating on one of the both sides such that an upper side of the annular flange is coated with the heat-sealable coating, the upper side faces away from the lid opening. The lid membrane is fastened to the lid ring by heat sealing to the upper side of the annular flange.
The can lid may further comprise a pull-open tab, for pulling the lid membrane off of the lid ring. The pull-open tab is fastened by laser welding to an upper side of the folded peripheral area of the lid membrane, and the upper side faces away from the lid opening.
An advantage of the can lid according to one embodiment of the invention is that it is even easier to open, than those of the pull-open tab type previously known.
Thus, in one aspect, the invention provides a can lid comprising a lid ring, for surrounding a lid opening, having on its inner periphery an annular flange, and a lid membrane having a peripheral area, which peripheral area is folded under to form a roll. The lid membrane is positioned on the lid ring for sealing the lid opening so as to be flat. A pull-open tab, for pulling the lid membrane off of the lid ring, is fastened along a fastening seam to an upper side of the roll of the lid membrane. The upper side of the roll faces away from the annular flange.
Advantageously, the fastening seam is a soldered seam or a laser weld seam.
In a preferred aspect, the lid membrane has an underside, and the peripheral area is folded under toward the annular flange to form a roll such that the end face of the lid membrane adjoins the underside of the lid membrane.
In another preferred aspect, the pull-open tab is fastened through one its ends to the fastening seam, such that the one end is folded about the roll and anchored in the roll.
In one aspect, the invention provides a can lid comprising a lid ring for attachment to a can and having an inwardly directed flange surrounding a lid opening. The annular flange is in the form of a flattened fold defined by a lower web portion and an upper web portion. The upper web portion is folded outwardly over the lower web portion so as to have a free end face outwardly directed relative to the lid opening. A lid membrane for closing the lid opening and having a peripheral portion terminating in a peripheral end face, is also part of the can lid. The peripheral portion is downwardly rolled over so that the peripheral end face lies in abutting relationship with an abutting surface. The lid membrane is detachably sealed to the upper web portion of the annular flange for subsequent removal by a user.
In another aspect, the invention provides a can lid comprising a lid ring for attachment to a can and having an inwardly directed flange surrounding a lid opening. The annular flange is in the form of a flattened fold defined by a lower web portion and an upper web portion. The upper web portion is folded outwardly over the lower web portion so as to have a free end face outwardly directed relative to the lid opening. At least the upper web portion has a heat-sealable coating thereon. A lid membrane for closing the lid opening and having a peripheral portion terminating in a peripheral end face has a heat-sealable coating on at least a lower face thereof. The peripheral portion is downwardly rolled over so that the peripheral end face lies in abutting relationship with an abutting surface. The lid membrane being detachably heat sealed to the upper web portion for subsequent removal by a user, and the heat-sealable coating extends between the peripheral end face and the abutting surface.
In a further aspect, the invention provides a method for producing a can lid as described herein. The method comprises the steps of folding the peripheral area of the lid membrane under; placing the folded peripheral area of the lid membrane onto the annular flange so that the folded peripheral area surrounds the annular flange; and fastening the lid membrane to an upper side of the annular flange, said upper side facing away from the lid opening.
In another aspect, the method comprises rolling the peripheral portion of the lid membrane downwardly over so that the peripheral end face lies in abutting relationship with an abutting surface, placing the rolled peripheral portion with the lid membrane onto the annular flange so that the rolled peripheral portion surrounds the annular flange, and detachably heat sealing the lid membrane to the upper web portion for subsequent removal by a user. The heat-sealable coating extends between the peripheral end face and the abutting surface.